Sharks have been in existence for more than 400 million years.
Although sharks generally appear to be very different from fish they are actually considered fish themselves.
What separates sharks from other species of fish is their cartilaginous skeleton which is made out of cartilage compared to the bones found in many species of fish.
Sharks also have an oil based liver which is used to provide the shark with buoyancy as well as several other differing characteristics unique to the shark species.
Sharks can be found in all of the worlds major oceans and may be seen swimming at depths of more than 2 miles underwater.
While almost all species of shark live in saltwater environments there are a few species such as the river shark and bull shark that have been known to live and thrive in fresh water environments.
In terms of diversity there are currently over 470 known species of shark in existence today which are split into at least 8 different suborders:
Sharks can vary greatly in size from the smallest shark (the dwarf lanternshark) which measures in at around 6 1/2 inches to the largest shark (the whale shark) which can grow to lengths of over 40 ft.
Common physical characteristics found in sharks include non fused pectoral fins, a cartilaginous skeleton, several sets of embedded replaceable teeth, 5 – 7 (uncovered) gills on the sides of its head and an unattached jaw.
When it comes to a sharks teeth the shape of its teeth can vary from dense flat teeth (often found on sharks that eat crustaceans such as krill and shrimp) which are used for crushing their prey to sharp needle-like teeth (often found on fish-eating sharks) which can be used to puncture and grip prey.
Sharks that hunt larger prey such as marine mammals (which can include dolphins and on rare occasions small whales) are known to have pointed lower teeth, which helps them grab their prey and triangular-shaped upper teeth that have serrated edges used for tearing their prey apart.
Sharks have several rows of replaceable teeth that generally get replaced one at a time, although there are a few species that may replace an entire row at one time.
It has been estimated that some sharks may replace tens of thousands of teeth (as much as 30,000) over the course of its lifetime.
Most sharks have 8 fins to help it maneuver through the ocean and a tail which is used to provide the shark with acceleration.
These fins may include left & right pectoral fins, first & second dorsal fins, a dorsal fin spine, a pelvic fin, an anal fin and a caudal fin.
Because of the sharks physical design it is unable to swim tail first and can only drift out-of-the-way of on coming objects and/or threats.
Sharks have 5 to 7 gills which are located on the sides of its head.
In order to breathe sharks extract oxygen from the water through their gills, however their gills are not designed to extract oxygen from the air so sharks are unable to breathe above the water and even if a shark could breathe above the water it lacks a rib cage and would be crushed under its own weight if it tried to survive outside of the ocean.
To help sharks with their buoyancy they have a large liver which is filled with oil containing squalene (a natural oily substances which is lighter than water) and light cartilage bones to help prevent them from sinking.
Sharks may also use a technique known as dynamic lift in which the shark uses his pectoral fins much like a bird uses its wings to maintain flight by flapping its wings.
This becomes especially important during periods of slow movement or stillness when a shark isn’t moving at all and needs additional aid due to a lack of forward propulsion.
Sharks can be seen eating a variety of prey which varies depending on the sharks size, social structure, teeth shape, size & formation and species.
Most sharks are carnivores and are known to eat a number of different species of fish and squid.
Some sharks are known to only consume benthic prey and crustaceans.
When it comes to hunting sharks have developed a number of different hunting methods to isolate and capture their food.
Basking sharks and mega-mouth sharks for example use a method known as filter feeding to capture their prey in which they swim towards their prey with their mouth open sucking up as much food as possible.
Sharks such as the wobbegong & angel shark use camouflage to catch their prey by surprise by staying still and blending in with their environment then striking ounce their prey is within range.
Many species are also known to hunt together using team oriented hunting strategies to isolate, stun, capture and eat their prey.
It’s also interesting to note that while some sharks use their teeth to grip and rip open their prey’s flesh other species rarely use their teeth and will consume their prey whole.
Sharks can be found swimming in all of the worlds major oceans, however most species will be found living exclusively in saltwater environments.
In deep waters sharks may be found swimming to depths of up to 10,000 feet, however it is rare to see them living at these depths.
Most sharks tend to limit their depth to around 7,000 ft or less.
As far as territory goes most sharks are known to travel from one location to another rarely staying in one spot for several years, however some species or individual sharks have been known to maintain a territorial area year after year.
Areas where a certain type of prey is abundant can affect a sharks likelihood of becoming territorial.
Since food is a big part of a sharks ability to survive many species can be found migrating to areas where their prey travels, so if their prey is likely to stay in a specific area then its possible that some sharks may choose to inhabit that area as well.
Enclosed or highly suitable environments may also contribute to a sharks desire to maintain a specific territory.
Unfortunately there many mixed views about whether or not sharks are generally territorial creatures, so its important to understand the influences of what can affect a sharks territorial behavior such as food, enclosed/highly hospitable environments and an aggressive or territorial nature.